Vhost support

So there doesn't seem to be any interest in some kind of
vhost_alias module so I'd like to try and write one but I
need a little help with the nginx codebase.
server {
listen 80;
server_name _;
location / {
root /var/www/$host;
}
}
If I use the above then I get this in the logs...
2011/01/29 16:09:13 [error] 32404#0:
*1 "/var/www/domain.org/index.html" is not found
(2: No such file or directory), client: 192.168.1.2,
server: _, request: "GET / HTTP/1.1", host: "domain.org"
(yes, I know the /var/www/domain.org directory does not exist)
This is pretty good but I want to reverse the domain.org $host
variable and provide, say, a $rhost variable of "org/domain".
I have an apache2 module that already does this so I just need
some orientation or assistance to find where in the nginx code
to do the same thing so any pointers would be appreciated.
Anyone care to offers some clues?
--markc